Hello again, sorry for double posting.
Odd though this sounds to me, I may not be playing the music through the SoundMAX card after all.
I'm using Bluetooth headphones (BSH10) connected using a Bluetooth adapter plugged into the USB. When I switch the headset on it seems to switch the Bluetooth Suite on, which then flips the in-use audio driver from SoundMAX to Bluetooth A2DP Source Device. I ran DXDiag against it, and it stated that there was no hardware buffer, and that the music is buffered using the software buffer (i.e. the driver, I assume).
Some
reading online reveals that mobile phones using bluetooth headsets can sometimes compress the audio stream to a smaller size to provide some security that the stream will fit into the phone's software buffer. Since bluetooth headsets are primarily designed for phones, it's not outwith the realm of possibility that the XP driver for this headset could be doing the same thing.
Since the previous version of XION doesn't have this problem, that would seem to point to something in the latest version (as noted probably to do with the introduction of the pitch slider) changing the way that the audio stream is sent to the driver.
I'll try testing the configuration tomorrow at work with a pair of old-fashioned wired headphones plugged into the SoundMAX card and see if I get the same issues.
I hope that may help with a diagnosis.